In sub-sea well drilling operations, it has been customary to test the blow-out preventers (BOPs) once a week. This is done by pulling the wear bushing (sometimes called "bore protector") from the sub-sea well head prior to running a plug tester into the well.
Part of the reason behind pulling the wear bushing is to check the extent of wear on the bushing bore to estimate the amount of wear that could exist in the bore of the smallest diameter well casing below the wear bushing which is suspended from the topmost casing hanger. If the wear bushing bore is worn, this indicates that the same degree of wear or possibly more wear could exist in the bore of the well casing immediately below the wear bushing. Excessive wear of this nature anywhere in the well below the BOP can result in a blow-out at the point where the drill pipe string has worn a groove through, or nearly through, the casing wall.
The object of the present invention is to provide a method for periodically testing the BOP without the necessity for pulling the wear bushing, thereby saving considerable time and cost compared to the prior art procedure. The present process is particularly advantageous in the deeper depths of the sea in which off-shore wells are now being drilled. Furthermore, in the prior art testing of the BOPs, without pulling the wear bushing, there is no reliable way of determining the degree of wear on pipe or casing below the first casing hanger.
In accordance with the essence of the present invention, a special test tool assembly is made up and is run into the well to land on a tapered seating surface of the wear bushing. After this landing, a dart for delivering energizing pressurized fluid to the test tool is dropped through the drill pipe. The test tool is then pressurized or energized to a pressure well above the pressure to be employed for testing the BOP, usually one thousand pounds above the BOP test pressure. While maintaining this energizing pressure on the test tool, the BOP can be tested except for the blind rams. After completing the testing of the BOP, pressure on the drill pipe is bled off, the dart is retrieved and this allows dry string retrieval of the test tool assembly to the floor of the rig. The test tool used in the process is of the type disclosed in U.S. Pat. No. 4,373,380, issued Feb. 15, 1983, to Mayo.
When the test tool has been retrieved, the thin metal lips of its seals are inspected for bulging or deformity. This gives a direct indication of the degree of wear in the bore of the well casing below the first casing hanger and wear bushing. The permanent deformation of the metal lips of the test tool seal is caused by these lips being forced outwardly into any wear groove or recess which may exist in the well casing when the tool is energized by pressure fluid delivered through the dart.
Other features and advantages of the invention will become apparent to those skilled in the art during the course of the following description.